Disease Loss Assessment for Azalea, Rhododendron, and Japanese Holly in North Carolina Nurseries. D. M. Benson, Associate Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. R. K. Jones, Professor, and K. R. Barker, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Plant Dis. 66:125-128. Accepted for publication 6 May 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-125.

Incidence of Phytophthora root rot of azalea caused by Phytophthora cinnamomi ranged from 1 to 19% with a mean of 16.9 ± 12.8% at 10 nurseries surveyed in North Carolina using a systematic sampling procedure. Tremendous variation in root rot incidence at the nurseries surveyed resulted in extremely variable population estimates for disease incidence. Incidence of Phytophthora dieback of hybrid rhododendron caused by Phytophthora spp. ranged from 0 to 12% at 10 nurseries surveyed, with a 6% incidence on a total plant population basis. Incidence of Phytophthora root rot of rhododendron caused by Phytophthora spp. ranged from 0 to 22%, with an incidence of 1.6% on a total plant population basis. Estimates for incidence of dieback and root rot of rhododendron were more reliable because the total plant population at each nursery was counted and scored for disease. Plant-parasitic nematodes, including Macroposthonia sp., Meloidogyne sp., and Tylenchorhynchus sp., were found in root and soil samples from field-grown plants at five Japanese holly nurseries surveyed. On a per plant basis, frequency of occurrence ranged from 4 to 100% at the nurseries depending on nematode species.

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